In rotary pumps or motors, it is usual to incorporate moving vanes, which have an axial or radial movement as the rotor turns to control the flow of fluid within the device and thereby obtain the pump or motor action. Movable parts in the rotor add complexities in the mechanism for actuating these parts and may result in failure because of the centrifugal load on these parts.
Hot gas engines presently in use are frequently of the gas turbine type and these have a narrow speed range for best performance. They are generally also high speed devices thus requiring extensive reduction gearing for driving low speed devices. A gas engine utilizing a rotary pump for a compressor and a similar rotary motor as the drive for the compressor and to produce additional energy for use has been a complex device and accordingly difficult to manufacture, service and overhaul. Simplified rotary pump/motors of matching capacity could produce a simplified gas engine that would have a wide speed range and could be easily assembled and disassembled.